Lysophosphatidic acid (LPA) is an extracellular signaling molecule with a broad range of physiologic effects. LPA may be rapidly produced at sites of inflammation, thrombosis, and vascular injury and has been proposed as a mediator of cardiovascular disease. LPA elicits effects by binding to a class of G protein- coupled receptors. In the vasculature, it may regulate smooth muscle function and cause activation of endothelial cells and platelets. The production of LPA in circulation is dependent tipon autotaxin (ATX), an enzyme with lysophospholipase D activity. ATX contains a somatomedin B-like (SMB) domain with an RGD sequence homologous to the integrin-binding region of vitronectin. This suggests that ATX may bind to integrin receptors thus localizing production of LPA in vicinity of membrane LPA receptors. My preliminary data indicates that activated platelets bind ATX in a 3 integrin-dependent manner. I hypothesize that the binding of ATX to activated platelet 3 integrins serves to increase LPA production by bringing ATX in proximity to its substrate, lysophosphatidylcholine. To test this hypothesis I propose two aims. First, I will define the mechanism by which ATX binds to activated platelets (Specific Aim 1). I propose that binding occurs via interaction of the RGD sequence on ATX with activated aVp3 and/or allbp3 on the platelet surface. To test this hypothesis I will use genetic, pharmacologic, and immunologic approaches. Second, I will evaluate the role of this interaction on ATX activity (Specific Aim 2). I will accomplish this by using tools established in my preliminary studies and in Specific Aim 1 to disrupt ATX binding and evaluate the effect of binding on lysophospholipase D activity both in vitro and in vivo. Our laboratory is uniquely well-prepared for such study as we have a great deal of experience in lysophospholipid signaling and metabolism. This work will provide novel insights into lysophospholipid signaling as it presents a mechanism of generating LPA directly at the surface of the targeted cell. Furthermore this will also provide a new therapeutic target for cardiovascular and other diseases in which LPA signaling has been implicated. The formation of a platelet clot is typically the final event leading to heart attacks and strokes, and anti-platelet drugs such as aspirin and Plavix have been a mainstay in treatment of cardiovascular disease. However, these medications are not effective in all people and oftentimes cause unnecessary bleeding. It is therefore important to study further mechanisms by which platelets are regulated so that safer and more effective therapeutics might be developed.